Photolithographic patterning techniques are commonly used in integrated circuit fabrication. Typically, ultraviolet light is transmitted through a photographic mask. The image of the mask is focused on the surface of an integrated circuit device under fabrication. The patterned light defines a spatially extended image that typically exposes a layer of photoresistive material formed on the surface of the device under fabrication. Using conventional integrated circuit fabrication techniques, the photoresistive layer, which has been exposed by the mask image, is then used to define etches or implants for subsequent fabrication steps.
Current photolithographic patterning systems for commercial integrated circuit fabrication use ultraviolet light (typically the I-line of mercury). Because an entire integrated circuit can be imaged with a single spatially extended image beam, these photolithographic patterning systems are referred to as photolithographic steppers.
As integrated circuits become more complex, the number of circuit elements increases and their size correspondingly decreases. As the circuit dimensions being patterned decrease, the resolution of a mask-image pattern must be increased. While the resolution of optical photolithographic patterning systems is being continually increased, patterning systems are available that achieve significantly greater image resolution than available (or likely to be available) from optical photolithographic patterning systems. One such patterning technique uses an electron beam that is scanned over the surface of a device under fabrication, and selectively blanked to create the desired pattern image.
Scanning electron beam patterning systems use a point source to create a narrow beam of electrons that is focused and scanned. These systems operate with wavelengths on the order of 10 nanometers, achieving significantly greater pattern-image resolution than is available from optical photolithographic systems that typically operate with wavelengths in the range of hundreds of nanometers.
The disadvantage of scanned e-beam patterning systems is that the scanning operation requires considerably more time to produce a pattern than the mask-stepping operation of optical photolithographic patterning systems. Consequently, despite the superior resolution available from scanned e-beam patterning systems, they are seldom used to directly write the patterns on commercial integrated circuits. Rather, these patterning systems are limited to fabricating prototypes or experimental devices, and to making the masks for conventional optical stepper systems.
Accordingly, a need exists for an extended source electron beam patterning system capable of imaging an entire pattern mask in a single-step operation. That is, a satisfactory electron beam imaging system would avoid scanning the electron beam.